The invention relates to a method for preparing granulated alkaline earth metal carbonate, to granulated alkaline earth metal carbonate obtainable thereby, and to its use in the glass industry.
Alkaline earth metal carbonate, especially barium carbonate and strontium carbonate, are used in the glass industry, for example in the manufacture of frontplates for television receivers. In this manner X-rays from cathode tubes can be absorbed.
One method for the production of very pure alkaline earth metal carbonates is the precipitation of alkaline earth metal hydroxides or alkaline earth metal sulfides with carbon dioxide or carbonates. In this process very fine powders are formed, which are hard to handle. The granulation of these powders has heretofore been performed by sintering at about 800.degree. C. in rotary kilns which are lined with inorganic refractory materials, e.g., with amorphous silicon dioxide, aluminosilicates or fire clay. In such kiln granulation processes it is absolutely impossible to prevent detritus of refractory material from contaminating the granules. As a result of these impurities, a considerable proportion of the frontplates produced must be considered unusable and must be remelted.
Adams et al., U.S. Pat. No. 4,888,161 describes a method in which the contamination of the carbonate by detritus of refractory material, which is to be attributed to the high sintering temperature of 800.degree. C., can be reduced. In this process, a suspension of the carbonate in water is first prepared, and an amount of a deflocculant sufficient to deflocculate the carbonate is added, preferably alkali metal salts or ammonium salts of acrylic acid or methacrylic acid or of phosphoric acid or polyphosphoric acid. The liquefied suspension is then dried in a spray dryer, and the resulting granular product is heated to 600.degree. to 700.degree. C. The type of heating used is described as not critical.
There remains a need for an improved method of producing granulated, high purity alkaline earth metal carbonate.